Studies of the mode of action of an irreversible inhibitor of catecholamine uptake are proposed. The studies will utilize rabbit aorta, rat brain and superior cervical ganglia in in vitro experiments where after prior exposure to the inhibitor, xylamine, 3H-norepinephrine accumulation and metabolism will be examined. In addition, experiments with 3H-labelled xylamine will be conducted to assess specific binding and its relationship to pharmacological effect. The exact molecular species involved in irreversible inhibition will also be determined by kinetic and synthetic procedures. Xylamine has also be shown to cause NE depletion. HPLC procedures have been developed for routine NE content determination and will be used to determine the mechanism for the depletion an its relationship to the inhibition of uptake.